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Question DetailsAsked on 10/5/2011

My kitchen floor has a dip in it. I see in the basement that there are wedges between the floor and the joist. How can this be fixed?

My kitchen floor has a dip in it. In the basement I see that the previous owner put wedges between the kitchen floor and the floor joist. The dip seems to be in the area where the HV/AC ducts are located. Is there a way to fix this? I thought about positioning lolly columns under the joist to bring the kitchen floor up to make it even. If I do this, would I need to take out the wedges?

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2 Answers


I have a pretty good "guess" but that's all anyone can do without actually going to your house and looking. I would encourage you to retain an architect to review the situation.

My guess: the floor joists are not adequate for the load, and the have "bowed". Perhaps they were never adequate. Perhaps there has been load added to the floor (ie: tile, additional flooring, heavier appliances, etc.). Perhaps the josts have been compromised (by best guess) by holes and notches being cut.

I would recommend first, adding a "sister joist". A new joist adjacent to the existing of the same, or deeper depth, anchored to the existing joist with screws staggered top and bottom, at 12" o.c.

Again, a sagging floor is serious. This is STRUCTURAL FAILURE. You really need to have a professional help you before the problem becomes more serious, or the floor fails.

Answered 8 years ago by Belles Architecture


I see this question is 4 years old - don't know why it showed up in today's questions list.

Anyway, I beg to differ with the other comment about sagging floors necessarily being a sign of structural failure. A normal wood joist floor built with 2x6 or 2x8's will sag typically about 1-2 inches per 16 foot span over the course of 30-50 years or so, and up to about 4 inches for a 32-40 foot unsupported span (which granted is rare) with 2x8 or 2x10 construction. Even wood trusses and joists sag - though plywood joists tend to do less so than dimensional lumber or LVL 9laminated veneer lumber) beams. In fact, the normal design standard (depending on states, type of construction, and year built) assumes a 1 in 80 to 1 in 240 deflection of the beams under load and creep - so 3/4 to 2-1/2" sag in a 16 foot span would be considered acceptable depending on criteria. Very old houses commonly see up to 4-6 inches of sag if left unsupported, though in most cases by the time you get over an inch or two people start putting intermediate posts, lolly columns, or cupporting beams or walls under the midpoints to minimize the sag.

As long as the sag is even and the actual framing members are not breaking or splitting apart, or cracking across the grain, an inch or two of sag in an older home is normal and NOT necessarily an indication of structural problems.

In your case, putting intermediate supports or a divider wall or arches under it might be the solution, or jacking them up and doubling up (sistering) the floor joists in some cases. In other cases, jacking them up and strengthening them with plywood facing nailed on at close centers, or converting to an I joist by adding a continuous steel or 2x4 bottom flange on them is the best solution. Depends on specific construction, number of utility penetrations in the way or passing through the joists, and whether there is a finished room below that would be interfered with by columns or a dividing wal, posts and beam, or arches. A structural engineer or architect can provide ideas and rough comparison of costs, and also a structural engineer (independently or working for an architect) can evaluate whether or not you have a structural issue or not.

The existing wedge situation is not going to make for a stable subfloor, because instead of being fully supported on the joists, the plank/plywood/OSB/particle board subfloor is only going to be supported on the wedges, so it will tend to be springy and probably start warping and getting wavy in short order.

The wedges should probably come out as part of any repair. Structurally, they should - the problem you will have is when they were put in the nails holding the subfloor to the joists were pulled partway out, so now if they are removed those nails will "pop out", lifting the flooring (or penetrating carpet), so unless the flooring is going to be removed too they are likely to be a problem. Also, because they were partly pulled, even if driven back in now, the subfloor is likely to be squeeky and somewhat bouncy if not fastened down with new fasteners.

Since you say seems worse where HVAC ducts are located, I would suspect some HVAC contractor ran amok (they tend to do that, especially since the sawzall was invented) and cut part of your joists out. If that is the case, there are remedial measures to repair the joists, or lolly columns or supporting studwall under the joists is a viable solution.

Answered 5 years ago by LCD

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